290 PHi:SlCAL PROPERTIES OF SOILS. 



to the sandy soils the power of yielding abundant crops of this kind of 

 grain. Almost every district can present examples of well cultivaled 

 fields, where the contrary is proved — and the wheat crops w'hich are 

 yearly reaped from the sandy plains of Belgium, demonstrate it on a 

 more extended scale. 



Chemically speaking, a soil will produce any crop abundantly, pro- 

 vided it contain an ample supply of all that the crop we wish to raise 

 may happen to require. But, in practice, soils which do not contain all 

 these substances plentifulljs are yet found to differ in their power of 

 yielding plentiful returns to the husbandman. Such differences arise 

 from the climate, the exposure, the colour, the fineness of the particles, 

 the lightness or porosity of the soil — from the quantity of moisture it is 

 capable of retaining, or from some other of its numerous physical pro- 

 perties. These physical properties, therefore, it is necessary shortly to 

 consider. 



§ 4. Of the physical properties of soils. 



To the physical properties of soils was formerly ascribed a mudi 

 more fundamental importance than we can now attach to them. Crome 

 and Schiibler regarded the fertility of a soil as entirely dependent upon 

 its physical properties. Influenced by this opinion, the former published 

 the results of an examination of numerous soils in the Prussian provin- 

 ces, which are now possessed of no scientific interest; because they 

 merely indicate the amount of clay, sand, and vegetable matter which 

 these soils severally contained.* The latter completed a very elaborate 

 examination of the physical properties of soils, which is very useful and 

 instructive ;f but the defective nature of which, in accounting for their 

 agricultural capabilities, became evident to the author himself, when the 

 more correct and scientific views of Sprengel, illustrated in the preced- 

 ing section, afterwards became known to him. In giving, therefore, 

 their due weight to the physical properties, we must not forget that in 

 nature they are subordinate to the chemical constitution of soils. Plants 

 may grow upon a soil, whatever its physical condition — if all the fo(xJ 

 they require be within their reach — while, howevej t^yourable the phy- 

 sical condition may be, nothing can vegetate in a heallhy manner, if the 

 soil be deficient in some necessary kind of food, or contain what is de- 

 structive to vegetable life. 



Of the physical properties of soils the most impQ«tant are their den- 

 sity, their power of absorbing and retaining water ancfair, their capillary 

 action, their colour, and their consistence or adhesive power. There 

 are one or two others, however, to which it will be necessary shortly to 

 advert. 



I. MECHANICAL RELATIONS OF SOILS. 



1°. The density and absolute weight of a soil. — Some soils are much 

 heavier than others, not merely in the ordinary sense of heavy and light, 

 as denoting clayey and sandy soils, but in reference to the absolute weight 

 of equal bulks. 



* Recorded in his Grunda'dize der AgricuUur Chemie. 

 t /»«r Boden und aein verhdltniss zu den Gewdchsen. 



